1. Field of the Invention
The present invention relates to a process for the hydrogenation of acetone to give isopropanol.
2. Description of the Background
Acetone is a large-volume industrial product and can be prepared in specific ways, e.g. by oxidation of propane, or as a coproduct in the Hook phenol synthesis.
In the Hook phenol synthesis, one molecule of acetone is obtained per molecule of phenol. The demand for phenol is very different from that for acetone. For example, phenol and acetone are consumed in a ratio of 2:1 in the synthesis of bisphenol A.
A possible downstream product of acetone is isopropanol which has a significantly broader range of use. A very significant proportion of the isopropanol is converted into ethers, in particular diisopropyl ether and tert-butyl isopropyl ether.
The conversion of acetone into isopropanol is generally conducted by catalytic hydrogenation. For the production of isopropanol ethers, processes of hydrogenation and etherification are combined. Thus, EP 0 694 518, EP 0 665 207, EP 0 652 200 and EP 0 661 257 disclose processes for preparing various isopropyl ethers. The disclosures of these patent applications involve the following process sequence:                a) Catalytic hydrogenation of an acetone-containing liquid phase.        b) Etherification of the resulting isopropanol over acid catalyst systems.        
The process steps a) and b) are conducted one after the other, i.e. without work-up of the product mixture obtained from a).
Furthermore, EP 0 665 207 teaches a single-stage process in which a) and b) are conducted by means of a suitable combination catalyst in a single reactor. Because of by-product formation (the processes are designed for the preparation of isopropyl ether), isolation of the isopropanol after the reaction step a) is very costly.
The process described in EP 0 379 323 is a better method of preparing isopropanol from acetone. In this process, acetone is catalytically hydrogenated at a temperature of from 20 to 200° C. at pressures of from 1 to 80 bar using, as a matter of necessity, a trickle reactor. Trickle reactors are used in order to create a high mass transfer area between liquid and gas. They therefore have to have a trickle surface having a large surface area. The quality of the isopropanol obtained and the amount of by-products is not discussed.
For many applications, isopropanol must not contain by-products such as isopropyl ether nor traces of solvent from the hydrogenation of acetone. This is particularly true in the case where isopropanol is used in medical and cosmetic applications for the preparation of downstream products where isopropanol of a very high degree of purity is required. High degrees of purity can be achieved on an industrial scale only upon the implementation of costly purification steps. Thus, for example, when isopropanol is prepared by introduction of water into propane, sulfur-containing compounds which are present in the isopropanol product can prevent its use in the cosmetic or pharmaceutical industry. Removal of these contaminating components is only possible by further treatment of the isopropanol with activated carbon, Al2O3 or metals such as copper or nickel. A need continues to exist for a method of producing higher purity isopropanol by the hydrogenation of acetone.